P2188: System Too Rich at Idle (Bank 1)
The engine is running rich on bank 1 mainly at idle, so the computer is pulling fuel out when the car is sitting still.
What P2188 means
P2188 is the rich idle version of P0172. The upstream oxygen sensor on bank 1 reports rich exhaust at idle, and the computer has cut fuel trim as far as it can. At idle, small sources of extra fuel matter a lot, because the engine needs so little fuel to begin with. A purge valve stuck open is a common cause, since it draws fuel vapor from the charcoal canister into the intake even when it should be closed. A leaking injector, high fuel pressure and a sensor that misleads the computer into adding fuel, such as a MAF reading high or a coolant sensor reading cold, can also cause it. RepairPal also lists a clogged air filter, spark plug problems, poor fuel and software that needs updating. Shops compare fuel trims at idle and cruise, pinch off or command closed the purge valve to see whether the idle improves, and run fuel pressure and injector leak down tests. Fixing it brings back smoother idle and better mileage.
Common symptoms
- Check engine light on
- Rough idle
- Fuel smell from the exhaust
- Increased fuel consumption
- Black soot at the tailpipe
Most common causes
- Leaking fuel injector
- EVAP purge valve stuck open
- Clogged air filter
- Faulty MAF or coolant temperature sensor
- Fuel pressure too high
- Engine computer software needing an update
What to check yourself first
Replace a dirty air filter. Check whether the idle gets worse right after refueling, which points to the purge valve. Look at the spark plugs for black, sooty deposits.
Typical fixes and what they cost
| Fix | Typical cost | Note |
|---|---|---|
| Replace EVAP purge valve | $210-$251 | A purge valve stuck open dumps fuel vapor into the engine at idle. |
| Replace fuel injector | $768-$953 | If an injector is leaking or dripping. |
| Fuel pressure test | $60-$88 | To check for high fuel pressure. |
| Replace mass airflow (MAF) sensor | $274-$381 | If the MAF reads more air than the engine is actually taking in at idle. |
Typical US price ranges for parts and labor, not quotes. Your shop should confirm the cause with a diagnostic before replacing parts.
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Related codes
- P2187 System Too Lean at Idle (Bank 1)
- P0172 System Too Rich (Bank 1)
- P0175 System Too Rich (Bank 2)
- P0496 Evaporative Emission System High Purge Flow
- P0101 Mass or Volume Air Flow "A" Circuit Range/Performance